The field of the invention is the hydrogenation of alkyl esters of saturated aliphatic carboxylic acids and the present invention is particularly concerned with reacting olefins with carbon monoxide and alkanol in the presence of a catalyst consisting of a cobalt compound and a promoter selected from pyridine, non-ortho-substituted alkylpyridine or mixtures thereof at elevated pressures and elevated temperatures, hydrogenating the esters produced and treating them with an acid ion exchanger.
The state of the art of such alkoxycarbonylation reactions may be ascertained by reference to U.S. Pat. Nos. 3,507,891; 3,906,016 and 4,041,057 and the article "Hydrocarboxymethylation--an Attractive Route from Olefins to Fatty Acid esters?" by Peter Hofmann et al as published in I & EC, Product Research & Development, Vol. 19, Sept. 1980, pp. 330-334, the disclosures of which are incorporated herein.
The state of the art of hydrogenation of esters may be ascertained by reference to the Kirk-Othmer, "Encyclopedia of Chemical Technology", vol. 8 (1966), pages 365-382, under the section entitled, "Esters, Organic", particularly pages 369-370 and F. Zymalkowsky's "Katalytische Hydrierungen", published by F. Enke, Stuttgart, Germany (1965).
Acid ion exchange resins useful in the present invention are disclosed in U.S. Pat. No. 4,168,390 and "Ullmanns Enzyklopaedie der Technischen Chemie", Chemie GmbH publishers, Weinheim/Bergstr., Germany (1977), 4th ed., vol. 13, pp. 279-346, "Ion Exchangers".
Examples of these acid ion exchange resins are LEWATIT (R) products manufactured by Bayer AG Leverkusen, West Germany, designated
LEWATIT SPC 108 H PA1 LEWATIT SPC 118 PA1 LEWATIT SC 102 H PA1 LEWATIT SC 104 H PA1 LEWATIT SC 108 H PA1 LEWATIT CNP 80
It is known that by reacting olefins with carbon monoxide and a compound having a replaceable hydrogen atom such as an alkanol in the presence of a catalyst containing a metal of Group VIII of the Periodic Table of elements and possibly a promotor, fatty acid esters can be produced as disclosed in J. Falbe, Synthesen mit Kohlenmonoxid, Springer publishers, Berlin, Heidelberg, New York (1967).
An especially preferred variation of this reaction, which is termed alkoxycarbonylation, is the conversion in the presence of cobalt catalysts. The rate, the selectivity and the yield in linear fatty acid esters of the cobalt reaction can be increased by adding promoters belonging to the pyridine class of compounds. Pyridine itself and also non-ortho-substituted alkylpyridines and mixtures thereof have been found particularly effective.
The carboxylic acid esters obtained by alkoxycarbonylation are products with many applications. These esters may be further processed into alcohols, for instance, among other substances. The alcohols made according to this process, because of the use of nitrogen-containing promoters (pyridine and/or non-orthosubstituted alkylpyridines) in the alkoxycarbonylation stage, are contaminated by slight amounts of nitrogen-containing compounds. Commercially produced alcohols, made for instance by hydroformylation, Ziegler synthesis reaction, paraffin oxidations or by fat splitting, as a rule do not contain such contaminants. It is appropriate therefore to prepare the products which are sequential to the carboxylic acid alkylesters obtained by alkoxycarbonylation, preferably alcohols, in such a manner that they are free or extensively free of nitrogen-containing compounds.
It is not possible to sufficiently eliminate the nitrogen-containing compounds by distilling the alcohols or the carboxylic acid esters used as the previous stage. Even when distillation columns with a higher number of trays or plates are used and high reflux ratios are observed, no more than a rather uniform distribution of the nitrogen compounds into all the distillate fractions is obtained.
Even when the alcohols or the carboxylic acid esters are treated with adsorbents, such as activated carbon, aluminum oxide of various activities or silica, no more than an inadequate elimination of the nitrogen contaminations can be achieved.
Lastly, the nitrogen contaminations can be only insufficiently removed if the carboxylic acid esters are treated with acid ion exchangers prior to hydrogenation.